Large quantities of natural gas are available in many areas of the world, and natural gas is predicted to outlast oil reserves by a significant margin. However, a significant amount of natural gas is situated in areas that are geographically remote from population and industrial centers. The costs of compression, transportation, and storage make its use economically unattractive. To improve the economics of natural gas use, much research has focused on the use of methane, the main component of natural gas, as a starting material for the production of higher hydrocarbons and hydrocarbon liquids, which are more easily transported and thus more economical. The conversion of methane to higher hydrocarbons or hydrocarbon liquids is typically carried out in two steps. In the first step, methane is converted into a mixture of carbon monoxide and hydrogen (i.e., synthesis gas or syngas). In a second step, the syngas is converted into the higher hydrocarbons via a process such as Fischer-Tropsch synthesis or alcohols via alcohol synthesis. An acceptable example of Fischer-Tropsch synthesis is disclosed in U.S. Pat. No. 6,333,294 to Chao et al., incorporated herein by reference.
Current industrial use of methane or natural gas as a chemical feedstock proceeds by the initial conversion of the feedstock to carbon monoxide and hydrogen by either steam reforming (the most widespread process), dry reforming, autothermal reforming, partial oxidation or catalytic partial oxidation. Examples of these processes are disclosed in Gunardson, Harold, INDUSTRIAL GASES IN PETROCHEMICAL PROCESSING 41-80 (1998), incorporated herein by reference. Steam reforming, dry reforming, and catalytic partial oxidation proceed according to the following reactions respectively: 
As is shown schematically in FIG. 1, in catalytic partial oxidation, the hydrocarbon feedstock is mixed with an oxygen source, such as air, oxygen-enriched air, or oxygen, and introduced to a catalyst as syngas feed stream 10 in the CPOX reactor 1 at elevated temperature and pressure. When the feedstock comprises primarily methane, the stoichiometric H2:CO molar ratio of the product of a pure CPOX reaction is 2:1. However, due to secondary reactions, the observed H2:CO molar ratio in the syngas product stream 20 is generally less than the stoichiometric ratio. The downstream conversion of the syngas to higher hydrocarbons (e.g., fuels boiling in the middle distillate range, such as kerosene and diesel fuel, and hydrocarbon waxes) via the Fischer-Tropsch or other synthesis reaction may require an H2:CO molar ratio greater than that observed in the syngas product stream 20. Thus, it is generally necessary to provide an additional amount of hydrogen 40 to the CPOX syngas product stream before introduction into the Fischer-Tropsch reactor 2. Examples of acceptable methods of producing and separating hydrogen are described in Gunardson at 41-110, incorporated herein by reference.
After the syngas is reacted into higher hydrocarbons (if reactor 2 is a Fischer-Tropsch reactor) or alcohols (if reactor 2 is an alcohol synthesis reactor) the gas effluent 50 is separated from the liquid product stream 30. The liquid product stream goes on for further processing (not shown). If reactor 2 is a Fischer-Tropsch reactor, the gas effluent 50 generally comprises methane, unreacted H2, unreacted CO and other impurities such as CO2 and other light hydrocarbons. If reactor 2 is an alcohol synthesis reactor, gas effluent generally comprises CO and H2.
It would generally be desirable to eliminate or reduce the amount of supplemental hydrogen added in supplemental hydrogen stream 40. Additionally, it would be desirable to recycle a Fischer-Tropsch effluent stream rich in methane to a CPOX reactor without the need to separate hydrogen from the effluent stream.